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Prospects for New Physics with Early LHC Data

Prospects for New Physics with Early LHC Data. Kevin Black Harvard University. Outline. Standard Model Current Status Brief motivation for ‘new’ physics Large Hadron Collider and the ATLAS Detector Experimental Challenges Muon Reconstruction with ATLAS

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Prospects for New Physics with Early LHC Data

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  1. Prospects for New Physics with Early LHC Data Kevin Black Harvard University

  2. Outline • Standard Model • Current Status • Brief motivation for ‘new’ physics • Large Hadron Collider and the ATLAS Detector • Experimental Challenges • Muon Reconstruction with ATLAS • Prospects for early new physics searches • Dilepton searches • Diboson final states • Physics with the top…

  3. The Standard Model

  4. Where is the Higgs? • Standard Model Higgs • - Indirect data prefers low • mass Higgs excluded by direct • searches • Tevatron limits approaching SM cross-sections…

  5. Although the SM enjoys wonderful (and some times amazing) agreement with experiment there are some theoretical issues For example – fine tuning to keep the Higgs light… Why ‘new’ physics? W,Z,g higgs top 2 2 2 mphys = m0 +gLcutoff • Many other open questions: • Why three generations? • What is dark matter/energy? • Baryon Asymmetry and CP violation …

  6. LHC pp collider Ldesign = 1034 cm-2 s-1 Linitial= 1033 cm-2 s-1 s = 14 TeV

  7. In a nutshell… World’s best microscope !

  8. Tracking: |h| < 2.5 , B = 2 T • - silicon pixels and strips • - transition radiation detector (e/pi) separation • Calorimetry: |h| < 5.0 • EM: Pb-Ar • Had: Fe-Scintillator (central) , Cu-W Ar (forward) • Muons: |h| < 2.7 • Air-core Toroids, Drift Tubes ‘General Purpose’ Detector - identify and measure Jets (including heavy flavor) Electrons, Muons, Taus Photons Need to reconstruct and I Identify from: ~ fraction of GeV a few TeV !

  9. Coming soon… Collisions later this year! KB

  10. x y Muon Reconstruction L B s ρ θ To measure a pT = 1 TeV track with 10% resolution in a magnetic field of L = 5 m and ∫Bdl = 3 Tm we should aim for a σ(χ) < 50μm detector resolution.A pT = 20 GeV is measured with 0.2% accuracy in the same detector. • RPC and TGC: Trigger the detector and measure the muons in the xy and Rz planes with an accuracy of several mm. • CSC: Measure the muonsinRz with ~80 μm accuracy and in xy with several mm. Cover 2<|η|<2.7 • MDT: Measure the muonsinRz with ~80 μm accuracy . Cover|η|<2 ATLAS is designed to have precision measurements From the spectrometer standalone!

  11. First measured point Calorimeter correction Refit @ vertex How do we reconstruct muons? rpc barrel  projection rpc rpc barrel RZ projection MDT

  12. Muon Reconstruction Performance • Excellent performance on Monte Carlo • Large Rapidity Acceptance • Great Standalone Resolution

  13. Current Status Barrel ~100% installed End Cap Data Acquisition and Trigger being commissioned Something something Concurrently, offline software being comissioned Results on Cosmics I

  14. Results on Cosmics II

  15. Challenges at the LHC:Splash Events at High Energy At ~> few hundred GeV muons have significant probability to radiate! -Causes inefficiency in reconstruction (1) due to pattern recognition failures (2) Poorly measured parameters in MS

  16. Large number of models (SUSY, Technicolor, GUT, Exradimensions, Little Higgs, …) Focus on Final States Many interesting possibilities Narrow in on most promising final states with ‘early; data Dilepton Resonances Think of the Z, Y, J/ ‘As simple as possible, but not simpler’ - AE Diboson final states Low Background, still relatively simple topology Physics with the top quark LHC as a ‘Top Factory’ New Physics at the LHC 2010 ATLAS ???

  17. Many models of BSM physics have new particles that would show up as dilepton resonances Z’ – GUT, Little Higgs Strongly Interacting theories Extra Dimensions Limits range from several hundred GeV to ~ 1 TeV Dilepton ResonancesAs of today… 2 Table of Various exclusion limits

  18. Simple two body analysis Select two high pt objects Compute invariant mass and (perhaps) scattering angle Estimate background from background region Challenges… Object Identification Parton Density Functions Higher order corrections Scale , Linearity of energy Extrapolation to high energy.. Alignment.. Dilepton Resonances Mass (GeV) New physics or something more mundane?? Detector Performance is critical, Turns a mountain into a molehill ! Mass (GeV)

  19. Extrapolation to High Pt.. • Need to know performance at high Pt • Reconstruction, Trigger, Object ID, Backgrounds, .. • Must we rely on monte carlo? • Need a way to connect to data Trigger Efficiency Reconstruction Efficiency

  20. UnderlyingEvent g q u u q d u d u Hard Scatter Parton Distribution Functions… • Could be subtle, need to understand prediction of SM • PDF and higher order corrections expected to be largest systematic… • Could have been new physics – turned out to be poorly constrained PDFs proton proton

  21. Electrons • Golden Mode • Excellent resolution • Small DY background

  22. Muons Data needed to exclude A 1 TeV Z’ -detector performance is crucial

  23. Photons

  24. Taus

  25. Technicolor with Dibosons

  26. 3 leptons pt > 10 GeV MET > 30 GeV Z boson reconstructed Leptonic HT > 150 GeV Event Selection

  27. Heavy Top Quarks

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